At some point in the next few years, this giant piece of machinery might pass under Capitol Hill, deep below your feet. This “cutter head” for one of the machines that will dig the twin tunnels connecting the future University of Washington light rail station to Capitol Hill’s Broadway station arrived at the Port of Tacoma before being trucked to the UW light rail construction site:
A 21-foot cutter head from one of the three Tunnel Boring Machines that will be used on the University Link light rail project was offloaded recently at the Port of Tacoma following a long trip from Germany. Two of the machines are now here and being assembled at Jesse Engineering in Tacoma. The third will arrive next spring.
Image: Sound Transit
This cutter will be one of two that bore their way up from Montlake, under Volunteer Park and through to Broadway as part of the $1.9 billion project. You can see the tunneling routes and more about the tunnel boring machines, here.
Tunneling begins from the University of Washington station site near Husky Stadium in 2011 but isn’t planned to reach Capitol Hill until sometime in 2012:
Two tunnel boring machines will be launched from the bottom of the station excavation about 1 month apart. The TBM’s will excavate an average of approximately 44 to 50 feet of tunnel per day. As they travel through the earth, the TBM’s also place the concrete rings that form the exterior structure of the tunnel. Dirt from the excavation travels through the machine and onto a conveyance system which brings it back out to the surface to be hauled away.
On Broadway, a tunnel boring machine will begin working its way from Capitol Hill to downtown:
A single tunnel boring machine (TBM) will be launched from the bottom of the station excavation. The TBM is scheduled to excavate an average of 40 feet of tunnel every day. As it bores through the ground, the TBM will also place the concrete rings that form the exterior surface of the tunnel. Dirt from the excavation travels through the machine and onto a conveyance system which brings it back out to the surface to be hauled away.
When the TBM reaches Pine Street, the TBM will be disassembled and transported back to the Station site, where it will be reassembled to dig the second tunnel between Capitol Hill and Pine Street. The tunneling is done in this direction because there is not sufficient room for all the equipment needed to extract the excavated dirt at Pine Street.
Meanwhile, Seattle is facing the early stages of planning for yet another massive tunneling project as part of the Viaduct replacement for the waterfront. December 13th is the deadline for public comment on the plan’s Environmental Impact Statement. It’s interesting from the CHS perspective to see anti-tunnel proponents making statements about the safety of tunneling in the city just as Sound Transit’s contractors move into the construction phase when the boring will begin beneath us. It might be worth a trip into early phases of Sound Transit’s University Link planning to learn more about what opposition arose then. In the meantime, if you were part of providing feedback at the time, please considering sharing what you remember from the process.
520 Tolling Hearing Monday Night
With tolls coming to the 520 bridge in spring 2011, the state is trying to find out what you think of rates that could have the standard driver paying $7 a day to drive back and forth across the bridge. There’s a hearing Monday night to discuss the proposed toll schedule :
- December 6, 2010: A public meeting will be held at: Sound Transit, Board Room, Union Station, 401 S. Jackson, Seattle, 6:30 – 8:30 p.m. No Action will be taken at this meeting.
- December 7, 2010: A public meeting will be held at: Bellevue City Hall, Council Chambers, 450 110th Avenue NE, Bellevue, from 6:30 – 8:30 p.m. No Action will be taken at this meeting.
January 5, 2011: The Commission will take Action on the rate proposal at this final hearing at: Sound Transit, Board Room, Union Station, 401 S. Jackson, Seattle, from 6:30 – 8:30 p.m.
CHS contributor Andrew Taylor also points out that tolls could be coming to “the mainland” with payment being discussed for the Arboretum.
As one of the resident CHS downtown-tunnel critics, I’ll tell you why I’m in favor of the Capitol Hill-U District tunnel and opposed to the one downtown.
* Size. The downtown tunnel will be larger, by quite a lot. (44 feet diameter vs 21, maybe?) As far as I know, the technology they’ll use to dig under downtown is untested and experimental.
* The soil downtown is terrible.
* The downtown tunnel would go under Pioneer Square, with many historically significant and fragile buildings. The contractors are trying to guarantee that no more than 3 inches of settlement will occur as they dig… but they don’t really know what will happen. The state has tried to find someone to insure them against building damage, and no one (not even Lloyd’s of London) will take the bet.
I’m not an expert on this stuff, and I would be glad to hear the other side of the issue, but it seems that there are significantly more risks to going under downtown than going under Capitol Hill.
As a critic, Uncle Vinny needs to get his facts straight.
SR-99 tunnel planned a 55 ft diameter not 44 ft
SR-99 tunnel will be deeper and below the poor soils that plague the viaduct. Soils will actually be similar to what SoundTransit U-Link tunnels will encounter.
Settlement is always a risk. Being deeper and in harder soils mitigates the risk but does not eliminate it. You wear a seat belt to mitigate the consequence of a crash but you may still crash and die.
Smart owners budget for risk events (15 to 30% typical). Insurance is not an appropriate way to budget for risk and involves too many lawyers.
Well, my facts aren’t that terrible… I mean, the 55-foot diameter is worse than I thought, I appreciate you helping me make my point!
The point about the soil is that in an earthquake, the entire downtown area is going to be jelly. Why run a tunnel through that mess? The tunnel under Capitol Hill is much deeper, and the soil it goes through is more solid. (Ok, that’s a guess… does anyone know if I’m right?)
Some risks you budget for, others you buy insurance for. Business owners and project managers do both. The state sought repeatedly to find someone to insure them against settlement problems with the tunnel (i.e., they were very concerned about it), and found that no one would accept the project.
I agree completely. I’m actually pretty worried about what happens downtown when they start that project. It could be a major disaster.
Vinny-
Yes, I believe the soil under capitol hill would be more solid because it is not made up of the soil and soot from “denny hill” that was washed down to the waterfront decades ago.
I used to think that the Denny regrade was part of the reason the soil for the tunnel would be bad, but I think Patches Pal is right… the tunnel will go much deeper than that. If you look at page 35 (page 126 of the report) here ( http://www.wsdot.wa.gov/NR/rdonlyres/CDE7BF6D-94D8-46BC-9A7F), you can see what part of the soil is “recent sand & silt” and what is glacial sand/silt or clay/silt. For the most part, the tunnel will go through glacial soil.
I thought I remembered hearing that in a big earthquake, Cap Hill will be better off than downtown… but maybe that’s just because of the recent landfilling in downtown? I would assume that the rest of the soil is the same across the region, more or less, since it all came from receding glaciers?